The present invention relates generally to a system and method for implementing rate shifting for wireless communications and more particularly to a system and method for implementing rate shifting for Wireless Voice Over Internet Protocol (VoIP).
Rate shifting has a significant impact on the performance of a Wireless Local Area Network (WLAN). Its goal is to reduce packet error rate by selecting an optimal data rate. It is often an effective means to respond to the change of channel conditions. However, shifting too conservatively or too slowly can reduce the network throughput, while shifting too aggressively can also cause excess packet errors and result in degradation in network performance. So designing an effective rate shifting algorithm is very challenging. This is especially true for Wireless Voice over IP (WVoIP) as the strict QoS (Quality of Service) requirement for voice traffic can not sustain a slow rate adaptation or a false rate shifting.
Rate shifting is beyond the scope of IEEE 802.11 standards. Many implementations of rate shifting algorithm are available and each has its preferred use scenarios. Commonly used rate shifting algorithms often trigger rate shifting when the number of retries hit some pre-determined retry limit. However, there are two causes for packet errors: poor channel conditions and the overload of a network. In the first case, the retry based rate shifting works quite well, but it fares badly for the second case since a down-shifting in a congested network will increase network congestion. Thus, there is a need for innovative rate shifting algorithms that can differentiate between causes of packet errors and can rate shift accordingly.